The invention relates to measuring instruments and particularly comprises an apparatus for measuring the flatness of an object.
In the past, profilometers having a stylus which rides on the surface of the magnetic disk have principally been used to measure disk flatness. For example, the Hommel T-20 profile Tester, as well as the DEKTAK II, Federal and Clevite profilometers have been used for this purpose. The use of such profilometers is undesirable, however, in that they disturb the surface of the disk. Moreover, deviations from straight line movements of the stylus caused, for example, by bearing wear or misalignment are interpreted as being the result of disk surface variations.
The invention avoids the problems of the prior art profilometer structures by employing a measuring technique for measuring the flatness of objects which self-corrects for translational deviations. The invention, moreover, is not limited to use with profilometer type styluses and in the preferred embodiment uses a pair of diametrically opposed capacitive probes. While capacitive measuring has been used in various applications as is shown by reference to U.S. Pat. Nos. 4,339,907; 4,297,634; 3,679,972; 3,671,857; 3,287,637; 3,278,843; 3,187,253, it has not heretofore been employed to measure the flatness of objects in the configuration of the present invention.